1897] NOTES AND COMMENTS 11 
division, and (2) by the formation of so-called auaxospores, which 
are usually the result of conjugation. The former method of 
division is of unusual interest in the diatoms, since, owing to the 
peculiar arrangement of their valves by which one fits inside the 
other, a formation of progressively smaller and smaller individuals 
is a necessary result of simple division. The growth in size of the 
valves is usually supposed to be impossible on account of their 
silicified nature. It is imagined, however, that the production of 
infinitely small individuals, which would obviously result from the 
continuance of such a method of division, is prevented by the in- 
terpolation of auxospore formation; by the latter means the diatom 
is given an opportunity of regaining its maximum size. 
Mr George Murray, in a paper entitled “ On the reproduction of 
some marine Diatoms” (Proc. Roy. Soc, Edin., Dec. 1896), has, 
however, thrown new light on reproduction in this group. The 
author has observed in some marine forms a very interesting and 
totally new method of division. This form of reproduction was 
observed in Coscinodiscus, Biddulphia, Choeboceros, &c., but was 
followed out most fully in the first-mentioned genus. In Coscino- 
discus the cell-contents divide by successive division into eight or 
sixteen portions, and these become rounded off and lie free in the 
mother cell like spores in a sporangium. Lach of these portions 
becomes invested with valves showing the characteristic markings, 
and in fact becomes a young Coscinodiscus. These young forms ulti- 
mately escape from the parent cell, and are found floating free in the 
water as packets of eight or sixteen small individuals enclosed in a 
delicate membrane; later on the several individuals themselves 
become completely free. It is by this method of division that the 
enormous quantities of marine diatoms, occurring in many waters at 
certain seasons, are doubtless produced. 
As mentioned above, diatoms are usually supposed to be incapable 
of superficial growth, owing to the silicified nature of their membrane ; 
but, as Mr Murray points out, this view is hardly well founded. 
At all events, it raises the question of the nature of the membranes 
produced by the young diatoms inside the old valves, These diatoms 
must obviously be much smaller than the parent, and so, in the 
absence of growth, continued reproduction by this method would have 
as disastrous an effect on the size of the species as the method of 
simple division, and would similarly necessitate the production of 
auxospores. With this question in view Mr Murray investigated 
the nature of the membrane of the daughter forms, and his con- 
clusion is that the valves are either not silicified or only incompletely 
so. There is thus nothing to prevent the further growth of these 
young diatoms to the full size of the species. That this later growth 
takes place is supported by observation, for the very small forms of 
